The subject matter disclosed herein relates to steam turbines. Specifically, the subject matter disclosed herein relates to alignment of steam turbines.
Steam turbines include static nozzle assemblies that direct flow of a working fluid into turbine buckets connected to a rotating rotor. The nozzle construction (including a plurality of nozzles, or “airfoils”) is sometimes referred to as a “diaphragm” or “nozzle assembly stage.” Steam turbine diaphragms include two halves, which are assembled around the rotor, creating horizontal joints between these two halves. Each turbine diaphragm stage is vertically supported by support bars, support lugs or support screws on each side of the diaphragm at the respective horizontal joints. The horizontal joints of the diaphragm also correspond to horizontal joints of the turbine casing, which surrounds the steam turbine diaphragm. Diaphragm centering (or, alignment) pins (or keys) are used to position the diaphragms in the transverse direction during installation. These centering pins are also designed to take the torque load generated by the diaphragm.
The centering pin is traditionally installed in an area of the diaphragm assembly with a small interference. The centering pin is traditionally cooled (e.g., frozen) to a point in which it contracts to fit in this area of small clearance. This often requires the use of dry ice or another severe cooling mechanism during installation, e.g., in the field. However, the unavailability and relatively high cost of these severe cooling mechanisms can be undesirable. Additionally, freezing and thawing of the centering pin can cause misalignment of the turbine diaphragm. Other pins are bolted into place, which causes other concerns. Boiling still allows for movement of the pin under loading in one direction. Further, having a small bolt hole in the turbine casing is undesirable due to stress concentration proximate the hole.